Materials to prevent or retard the advance of flame are useful, particularly where it is desired to provide additional escape time for persons trapped in confined spaces by fire. An especially critical field of use for such materials is in vehicles used for mass transportation (e.g., airplanes, busses, trains) where relatively large numbers of people are confined within a relatively small space.
Numerous materials are known for preventing or retarding the advance of flame. For example, flexible sheet materials that employ intumescent materials are disclosed in U.S. Pat. No. 3,916,057 and British Pat. No. 1,513,808. Sheet materials that incorporate exfoliated or "popped" mica are disclosed in U.S. Pat. No. 3,001,571. Sheet materials that incorporate vermiculite are disclosed in U.S. Pat. Nos. 2,204,581 and 3,434,917.
Endothermal sheet materials are described in U.S. Pat. No. 3,144,840. These materials comprise a metal film adhesively bonded to a flexible backing. An endothermal layer is bonded to the side of the flexible backing opposite the metal film. The endothermal layer comprises an organic binder and an endothermic filler.
The foregoing sheet materials all suffer from at least one serious disadvantage, that is, they are relatively dense or "heavy". Consequently, they are not suited for use in the transportation field where added weight can significantly reduce fuel efficiency.
The present invention overcomes this drawback by providing a light weight sheet material that possesses excellent flame barrier properties. The flame barrier properties of the invention are demonstrated by its ability to retain sufficient structural integrity to prevent the flame from breaking through it for at least 30 minutes even though it may be charred by the flame. It has been found that this can be achieved without the use of either an intumescent material or a flame retardant. Details of the test utilized to test the flame barrier characteristics of the sheet are described more fully hereinafter.
The weight and flame barrier properties of the sheets render them useful in a variety of applications. For example, the sheet is useful in airplane escape slides, engine housings and pylons, cargo compartments, and fuselages.
Additionally, it has been found that the sheet of the invention possesses good low frequency noise absorption characteristics thereby rendering it useful as an acoustic barrier. This is surprising since the sheet is light weight and because it is usually necessary to utilize much heavier materials to achieve similar acoustic damping.